The invention is particularly concerned with processing tanks which are of the low volume type. A low volume or thin volume tank is particularly useful in photographic processing apparatus since imagewise exposed material which is being processed is passed along a path of very narrow dimensions which is filled with a processing liquid. Many of the liquids used are unstable and therefore have to be used very swiftly. If a conventional tank of processing solution is used and material being processed is not passed through it continuously, after a short period the whole tank of solution will have to be disposed of and fresh solution inserted for processing of the next batch of imagewise material. This can be extremely expensive since the solution is not being used to its maximum effect and can also give rise to other problems as the solution which is discarded will have to be treated before it can be environmentally acceptable and the treatment of large quantities of liquid becomes in itself a problem and expensive.
The principle of using a low volume tank has been known for some time and in U.S. Pat. No. 717,021 a narrow passage is disclosed which is defined between two blocks of material and photographic material to be processed is passed from external rollers through this narrow passage and is immersed in solution contained in the passage. The solution is constantly topped up by an automatic feed reservoir which feeds solution into the bottom of the passage. One of the problems arising from this type of narrow passage treatment is that the material being processed has to be pushed through by the feed rollers at the entrance to the narrow passage. Generally as the material is processed in the solution its physical nature changes and it becomes soft and clearly cannot be pushed very well over a long passage.
It has been suggested, for example in U.S. Pat. No. 4,736,222, that a leader should be attached to the material being processed. In this patent specification two strips of film are connected to a leader and the leader itself has central apertures which are engaged by drive sprockets of a timing chain in a tank. The leader pulls the film through the solution in the tank, round the bottom roller and out of the tank. The whole drive mechanism is basically immersed in the solution of the tank and this may cause corrosion with subsequent jamming or breakage of the drive mechanism and chemical contamination of the solution. Other prior art arrangements are described in GB-A-491479 and DE-A-3230175.
The disadvantages thus arise with the use of these known thin volume of processing apparatus that if an occurrence such as the material being processed jams in the tank, the whole of the process has to be interrupted for a substantial period while the whole of the apparatus is drained and taken apart to remove the blockage and then reassembled. Furthermore, by the inclusion of the drive mechanism within the solution, problems arising from corrosion are likely to give more frequent need for the machine to be taken to pieces for cleaning and replacement of parts. Also, as the drive passes through the solution surface it picks up solution and agitates the surface, this gives rise to increased chemical degradation by oxidisation, increased losses by evaporation and precipitation of hard crystals which could physically damage film. This down-time and solution wastage can be very expensive in modern processing commercial operations where it is necessary to ensure a steady and continuous throughput of material being processed in order to maximise the capital costs of the equipment.
It is an object of the present invention, therefore, to provide a photographic processing tank for use in low volume processing apparatus which reduces the risk of corrosion oxidisation and precipitation occurring and which enables any problems arising from jamming of the material or any other problem with the tank swiftly to be dealt with without causing a long delay in the photographic process thereby substantially minimising the down-time of the apparatus.